Update: I was unfortunately not aware of Shamus Young's severe criticism of Fallout 3 available here to link in the original piece and I regret that. It dovetails rather nicely with what I've written and it's much better executed than my piece. I strongly recommend anyone...

Cloud & Tifa's 3rd costumes:
To get Cloud's 3rd costume, beat the game with Yuffie. To get Tifa's, beat the
game with Vincent. To select these costumes, hold Down when selecting Cloud
or Tifa.

Even more costumes:
Fulfill the following 8 conditions to unlock extra costumes. The order is not
important, though the costume you enable is fixed (ie. Yoko is always the first
new costume, regardless of which condition you meet). Once you've unlocked a
third costume, press Down while selecting a character to use it.

- Beat arcade mode with any character without continuing
- Beat arcade mode and get Ehrgeiz with any character
- Perform a 10-hit combo in practice mode
- Get 35,000 points in Battle Beach mini game
- Get 2,000 points in Infinite Battle mode
- Enable all FMVs in the movie player
- Get a perfect score in Evil panel (computer must have 0 panels)
- Beat computer in Battle Runner on any level with any number of laps

Taunting:
To taunt, press Select and a direction on the D-pad. Some characters have more
than one.

Alternate Vincent Picture:
At the Character Select screen, highlight a character preceding Vincent. Press
Up on the D-pad, then Up-Left or Up-Right, then Left or Right (like a 'fireball'
move). You'll see Vincent as a Turk.

Alternate Opening FMV:
Let the opening loop several times, and eventually you will see the alternate
opening.

Extra Battles:
Fight through Arcade mode and beat Sasuke in less than 3 minutes 20 seconds.
If you do this, you will run through the second gate to fight Cloud and Tifa
before Django.

Each character has only one ending (except Han - see below), so it doesn't
really matter whether or not you kill the final boss.

Han's Good Ending:
Han is the only character to have two endings. To get the good ending, you have
to beat the final boss before the credits stop rolling. To beat the final boss,
you must break open the two boxes which will reveal two pieces of the sword.
Throw the two pieces of the sword at the boss, who will explode. Now quickly
run around gathering all of the items, including Han's leg. Viola!

Hints

Easy Dajango:
Select Cloud and when fighting Dajango, just get him in the corner and keep
pressing X for a nice cheap defeat, but watch out for that roll attack!

Find the Golden Axe:
Go down the well in The Forsaken Dungeon right before the Octopus you should
find it.